Hypertensive disorders complicate an estimated 6-8% of all pregnancies and are a significant source of fetal and maternal morbidity and mortality. Approximately 3-4% of all pregnant women will be exposed to antihypertensive medications during pregnancy. The antihypertensive most commonly used in pregnancy in the United States is methyldopa; however, it is an older, often poorly tolerated medication. It may be an inferior therapy with respect to important pregnancy outcomes compared to other classes of agents including alpha-beta blockers, beta blockers, and calcium channel blockers. Yet, for each of these other classes, important fetal safety concerns have been raised. The primary goal of the proposed project is therefore to evaluate the comparative safety and effectiveness of each of these commonly used agents relative to methyldopa. The clinical question this study aims to address is: If a patient requires an outpatient antihypertensive during pregnancy for pre-existing or gestational hypertension, what is the safest agent for the fetus, and the one most likely to assure a good pregnancy outcome? We will also examine the safety of first trimester exposure to thiazide diuretics and angiotensin converting enzyme inhibitors, which are the most common types of antihypertensives used in women of reproductive age outside of pregnancy and thus common first trimester exposures. This analysis will address the clinical question: For a woman in whom pregnancy is planned or possible, which agents can be safely used given the potential for early fetal exposure to the medication? The study will be performed using a pregnancy cohort obtained from the Medicaid Analytic Extract (MAX), a large population-based claims database. Using this dataset, we have developed a cohort of over 1.1 million pregnancies with longitudinal data that span from the pre-pregnancy to the postpartum periods. This cohort is linked to outpatient pharmacy claims and fetal records making it an exceptionally well-suited data source for the kind of study we propose. I will perform the proposed research within the well developed infrastructure of the Division of Pharmacoepidemiology and Pharmacoeconomics (The Division) at the Brigham and Women's Hospital. The Division has a long track record of producing outstanding drug safety and effectiveness research using observational data sources. I will work with an interdisciplinary team of mentors and collaborators drawn from across institutions at Harvard University that have deep expertise and national/international reputations in epidemiological and statistical methods, perinatal pharmacoepidemiology, high-risk obstetrics, hypertensive diseases, and drug policy. This research work will be complemented by formal coursework at the Harvard School of Public Health and frequent seminars and lab meetings at the Division. This combination of intensive research, mentoring, and formal education will provide the necessary background for me to become a successful, independent researcher in obstetric pharmacoepidemiology.